convertLatLngToSphere.js

const radians = deg => deg * Math.PI / 180

// @param {Number} z  Offset from radius
export default function convertLatLngToSphere (lat, lng, baseRadius, z) {
  // radians
  const phi = radians(lat)
  const theta = radians(lng - 180)
  
  const radius = baseRadius + z
  
  return [
    -radius * Math.cos(phi) * Math.cos(theta),  // x
    radius * Math.sin(phi),                     // y
    radius * Math.cos(phi) * Math.sin(theta)    // z
  ]
}